In recent years, displays in image display devices, such as television devices, are being shifted from conventional cathode-ray tube displays to thin display devices using thin displays, such as liquid crystal panels and plasma display panels. With the thin displays, thicknesses of the image display devices can be decreased. Liquid crystal panels used for the liquid crystal display device do not emit light. Therefore, liquid crystal display devices including liquid crystal panels require backlight devices. An edge-light type backlight device has been known as an example of such a backlight device. In the edge-light type backlight device, a light entrance surface is included on a side surface of a light guide plate and light sources such as LEDs are arranged near the side surface of the light guide plate.
In the above edge-light type backlight device, the light guide plate may thermally expands or shrinks due to heat generated near the light sources and this may change a distance between the light sources and the light entrance surface of the light guide plate. In a configuration in which a light source board is held to a casing such as a chassis and a plurality of light sources are arranged on the light source board, if precision in size of the casings may vary, variation occurs in a distance between components on the surface of the light source board and the light entrance surface of the light guide plate. Accordingly, a distance between each light source and the light entrance surface of the light guide plate may not be constant. If the distance between each light source and the light entrance surface of the light guide plate is not kept constant, light entrance efficiency of light from the light sources being incident on the light entrance surface of the light guide plate may vary, and good optical properties are not maintained.
Patent Document 1 describes an edge-light type planar light lighting device in which variations in the distance between the light guide plate and the light entrance surface are less likely to occur. In such a planar light lighting device, a transparent spacer is arranged between the light sources and the light entrance surface. With such a configuration, a distance between the light sources and the light entrance surface is fixed and the distance between the light sources and the light entrance surface is maintained constant.